He said the accused man's relatives had told the authorities he was insane and that they claimed Mr Rahman had said he heard strange voices in his head.

The judge also said it was not clear if the accused was really an Afghan or a citizen of another country.

Mr Rahman has lived outside Afghanistan for 16 years and is believed to have converted to Christianity during a stay in Germany.

It is because of this, the judge said, that he had asked the prosecution to examine Mr Rahman's situation.

Prison move

The Afghan government has come under increasing international pressure, especially from its Western allies, over the case and the BBC's Sanjoy Majumder in Kabul says it has been anxious to resolve the situation before it gets out of hand.

Mr Karzai has personally intervened in the case and several top level meetings have been held over the past two days to resolve the issue.

Dropping the case because of technicalities would offer the government a way out of the crisis, our correspondent says.

On Sunday officials said Mr Rahman had been moved to the notorious Pul-e-Charki prison on the outskirts of Kabul.

The maximum security facility is a vast prison complex built in the 1970s and is used to house common criminals as well as hundreds of Taleban and al-Qaeda militants.